The development of acquired immunity to the prototypic facultative intracellular parasite L. monocytogenes is associated with T cell dependent production of macrophage activating factors. The immune mechanism as determined by adoptive transfer methods identifies the responding T cell population as members of the subset of cells expressing the Ly 1+2+ phenotype. It has also been established that this adoptively transferred immunity is short-lived. We have recently established that the interval of transferred immunity can be significantly lenghtened and resistance increased to levels comparable with that seen in actively immunized animals. This more active and longer lived cell population can be obtained from short term tissue culture of spleen cells obtained from immune donors. The dramatic increase in the level and duration of the passively acquired immune state is associated with a Ly 1+2- T cell subset with not apparent activity retained within the Ly 1+2+ cell population. Our proposed studies will focus on the nature of the immunoregulation that is responsible for the dramatic shift in the function and apparent phenotypic change of the cells obtained from the in vitro culture. For this analysis we will evaluate the culture conditions that lead to cells with enhanced transfer activity and will record the temporal appearance of transfer active cells in culture as well as the cell cycle and cell cooperation requirements. In additional studies we will investigate the interaction of the transfer active cells with the recipient environment. Finally, we will attempt to correlate the immunologic status of the donor with the appearance of enhanced transfer activity acquired by cells following in vitro culture.